methods of melting

8/7/2019 Methods of melting

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METHODS OF MELTINGAnil Kumar. Garikapati


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INTRODUCTION

There are a no of methods available for melting

the foundry alloys such as,

Pit or crucible furnace,

Open hearth furnace, Rotary furnace,

Cupola furnace,

Electric furnaces,

The choice of the furnace depends on the amountand the type of alloy being melted.


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CUPOLAFURNACE

Cylindrical type of furnace for producing moltenCAST iron,

Lined with heat resisting (refractory ) bricks.

The shell is made of steel plate of 8mm to 10mm.

Dimensions of a cupola: The c/s area of a cupola depends on the o/p of themolten metal. And is det. By using the followingformula:=Ac

The height of the cupola is taken 3 to5 times the

diameter of the cupola. The common dimensions of the cupola are;

1.Outside dia- 900 to 2700mm

2.Inside dia - 500 to 2100mm

3.Height- upto12m


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Ingredients used inCupola

Ironwaste

Foundrywaste

Scrap

CarbonSilicon

Manganese

Feldspar

Sulphur

Pig Iron(main

charge)


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VARIOUS ZONES OF CUPOLA

Well or crucible.

Tuyer zone.

Combustion zone.

Reducing zone.

Melting zone.

Preheating zone


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COMBUSTION ZONE

Combustion if fuel takes place by oxygen of air

blast & produce lot of heat.

The reaction is Exothermic and the highest

temperatures are developed in this zone. The temperatures may reach 1600 degrees to

1700 degrees.

These heat transferred to other parts of the

furnace. Carbon, silicon & manganese are oxidised to

produce heat.

The reactions are,


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REDUCING ZONE

The Co2 Flowing upwards through this zone

reacts with hot cocke and the reaction is

endothermic.

The reaction is ,Co2 + C (coke) -> 2Co Heat.

Because of this reaction , the temperature in the

reducing zone gets reduced to about 1200

degrees. However , the metal charge (iron and other

elements ) above will be protected from

oxidisation.


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MELTING ZONE

This layer includes the the first layer of iron

above the initial coke bed.

In this zone ,the charge starts melting and

trickling through the coke to the bottom of thecupola,

A significant of the carbon pick up by metal also

occurs in this zone.

The reaction takes place is,3Fe + 2 Co Fe3 C +Co2


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OTHER ZONES

Preheating zone:-

Includes Charge And get preheated

Moisture and volatile matter are evaporated

The temperatures are here are 1090 degrees

Well:-

The molten metal gets collected here

This also known as Crucible

Stack:-

Carries the combustion gases


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DESCRIPTION

Shell

Spark arrester

Refractory lining

Charging door Charging platform

Wind box or blast pipe

Tuyeres

Slag spout Sand bottom

Tap hole

Legs & prop


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Charge

Metallicmaterials

Fuel

Fluxes


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CHARGE

Metallic materials

Pig iron of various grades.

Cast iron ,&

Steel crap,

Foundry scrap.

Fuel

Foundry coke

Anthracite coke .

FluxesA flux is a substance which react with

slag(accumulations of oxides and other unwantedmaterials)to lower its melting points

The fluxes used are Limestone, Dolomite


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OPERATION

Should be thoroughly dried before drying

A layer of sand (150mm) is placed over the doors andsloped towards the tap holes

Initially the kindling wood is fired

Coke bed is made (700 to 800mm)

Then coke and charge is added alternatively

The tuyeres are opened gradually to intensifies gradualcombustion

Lime stone =2 to 4%

Coke= 8 to 12 % , &

The metal is added alternatively The first molten metal would appear in the tap hole within

10 to 15 minutes

When the well or the crucible is filled the slag is firstdrained off.


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Initial cost is low compared toother

Maintenance is easy andeconomic

Operation Cost is low

Low space is required

compared to otherRun for long time

Composition of the melt can becontrolled

Temperature of the melt canbe controlled

Limitations

Metal purity cannot bemaintained

Temperature is difficult tocontrol


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CRUCIBLE FURNACE

methods of melting

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